Metabolic Profiling of S-praziquantel: Structure Elucidation Using the Crystalline Sponge Method in Combination with Mass Spectrometry and Nuclear Magnetic Resonance

Praziquantel (PZQ) is the drug of choice for treatment of the neglected tropical disease schistosomiasis. Although the drug has been extensively used over several decades and its metabolism well studied (several oxidative metabolites are known from literature), the knowledge of the complete structure of some of its metabolites remains elusive. Conventional techniques, such as nuclear magnetic resonance or liquid chromatography mass spectrometry were used in the past to investigate phase I and phase II metabolites of PZQ. These techniques are either limited to provide the complete molecular structure (liquid chromatography mass spectrometry) or require large amount of sample material (NMR), which are not always available when in vitro systems are used for investigation of the metabolites. In this study, we describe new structures of S-PZQ metabolites generated in vitro from human liver microsomes using the crystalline sponge method. After chromatographic separation and purification of the oxidative metabolites, ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry analysis was conducted to narrow down the position of oxidation to a certain part of the molecule. To determine the exact position of hydroxylation, singe-crystal X-ray diffraction analysis of the crystalline sponges and absorbed analyte was used to identify the structure of S-PZQ and its metabolites. The crystalline sponge method allowed for complete structure elucidation of the known metabolites S-trans-4'-hydroxy-PZQ (M1), S-cis-4'-hydroxy-PZQ (M2) and S-/R-11b-hydroxy-PZQ (M6) as well as the unknown metabolites S-9-hydroxy-PZQ (M3) and S-7-hydroxy-S-PZQ (M4). For comparison of structural elucidation techniques, one metabolite (M3) was additionally analyzed using NMR. SIGNIFICANCE STATEMENT: The information content of the metabolic pathway of praziquantel is still limited. The crystalline sponge method allowed the complete structural elucidation of three known and two unknown metabolites of S-praziquantel, using only trace amounts of analyte material, as demonstrated in this study

Quantum Dimensional Zeeman Effect in the Magneto-optical Absorption Spectrum for Quantum Dot - Impurity Center Systems

Magneto-optical properties of the quantum dot - impurity center (QD-IC) systems synthesized in a transparent dielectric matrix are considered. For the QD one-electron state description the parabolic model of the confinement potential is used. Within the framework of zero-range potential model and the effective mass approach, the light impurity absorption coefficient for the case of transversal polarization with respect to the applied magnetic field direction, with consideration of the QD size dispersion, has been analytically calculated. It is shown that for the case of transversal polarization the light impurity absorption spectrum is characterized by the quantum dimensional Zeeman effect.Comment: 18 pages, 1 figure, PDF fil

Magnetic and magneto-optic properties of thin films of the Heusler alloy PtMnSb

SIGLEAvailable from British Library Document Supply Centre- DSC:DX176679 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Magnetism and morphology of Fe/Cu(111) films below two-dimensional percolation

The magnetic properties of g-iron films on Cu(111) below the two-dimensional percolation threshold of about 1.4 monolayer are investigated. Iron on flat Cu(111) surfaces forms triangular patches, while it forms stripes along step edges on vicinal surfaces. The films exhibit an easy magnetization axis perpendicular to the film plane and magnetic hysteresis at sufficiently low temperatures. The magnetization curves of the triangular iron patches are discussed in terms of Ising superparamagnetism. From Kerr hysteresis loops, we deduce that the first anisotropy constant K1 in the superparamagnetic films is of order 0.345±0.020 MJ/m3

Magnetism in one dimension: Fe on Cu(111)

The magnetism and the morphology of one-dimensional Fe stripes on a Cu(111) vicinal surface with perpendicular magnetization are investigated. Scanning tunneling microscopy shows that the Fe stripes have nanometer width and are aligned in parallel along the [011] direction. From the magnetization curves it is inferred that the stripes exhibit a ferromagnetic behavior well below the nominal thickness of one monolayer. In contrast to two-dimensional films, the magnetization of the stripes is not only temperature but also time dependent. The dynamics of the stripes have been described by a micromagnetic Ising model with Glauber dynamics, yielding an effective anisotropy constant K1 of 0.65±0.15 M J/m3

Effect of silicon crystal structure on spin transmission through spin electronic devices

Spin injection into and spin transport through silicon spacer layers in iron/silicon/cobalt structures has been investigated. Ultrahigh vacuum evaporated silicon spacers of varying crystal quality from amorphous to epitaxial of thicknesses from 10 to 200 Angstrom were shown to improve their electrical conduction with increasing crystallinity, but no spin dependent transport was observed through the structure. Silicon and iron interdiffusion was also observed at the interfacial region. Device quality silicon was studied using 460 and 540 mu m doped silicon wafers of resistivity 0.1 and 1 Omega cm, respectively, polished on both sides, onto which were deposited iron and cobalt layers. Sharp metal-semiconductor interfaces were achieved in this way, but no spin dependent transport, putting an upper limit on the spin diffusion length in device quality silicon wafers. (C) 2000 American Institute of Physics. [S0021-8979(00)92808-1]

In-plane anisotropy and reversed spin reorientation of fcc Fe ultrathin films on Cu(100) by pulsed-laser deposition

Fe ultrathin films on Cu(100) have been prepared by pulsed laser deposition (PLD). These films show good layer-by-layer morphology and an almost ideal fcc structure at all thicknesses below 10 ML. Above 10 ML the films transform into bcc(110) structure. The magnetization of the PLD Fe films lies in-plane at low thickness (2 to 5 ML), and undergo a reversed spin reorientation switching to perpendicular at higher thickness